Lithium Isotope Separation Research Articles

Calix[4]arene-decorated polymers of intrinsic microporosity for lithium isotopes separation

Due to the importance of lithium isotopes in the nuclear energy industry, there are increasing number of researchs on the lithium isotopes separation in recent years. However, the adsorbents used for lithium isotopes separation suffer from the low adsorption capacity and isotopes separation factor in aqueous phase, and is difficult to meet the requirements for industrial lithium isotopes production. In this work, two types of calix[4]arenes with different rim groups were incorporated into the polymer backbone. Both calix[4]arene decorated PIMs exhibited good lithium adsorption capacities in aqueous phase. Among them, 4-tert-butyl-calix[4]arene decorated PIM showed excellent lithium isotopes separation performance with a maximum lithium adsorption capacity of 67.99 mg·g−1 and an isotopes separation factor of 1.034 ± 0.003 in aqueous phase. The ease of preparing and stable cycling performance makes it potentially useful for industrial lithium isotopes production.

Research progress on lithium isotopes separation by chemical exchange with crown ethers decorated materials

The separation of lithium isotopes (6Li and 7Li) is of great importance for the nuclear industry. The lithium amalgam method is the only lithium isotopes separation process in industry, and the extensive use of mercury has raised concerns about its potential environmental hazards, which have prompted the search for more efficient and environmentally friendly alternatives. Crown ethers can bind lithium ions highly selectively and separate lithium isotopes effectively. A chemical exchange-based lithium isotopes separation method using crown ether decorated materials could be a viable and cost-effective alternative to the lithium amalgam method. In this review, we provide a systematic summary of the recent advances in lithium isotopes separation using crown ether decorated materials.

Separation of Lithium Isotopes by Electromigration with Aqueous-Organic Biphase System

Separation of Lithium Isotopes by Electromigration with Aqueous-Organic Biphase System

Benzo-15-Crown-5 Functionalized Ionic Liquids with Enhanced Stability for Effective Separation of Lithium Isotopes: The Effect of Alkyl Chain Length

Benzo-15-Crown-5 Functionalized Ionic Liquids with Enhanced Stability for Effective Separation of Lithium Isotopes: The Effect of Alkyl Chain Length

Electromigration separation of lithium isotopes with B12C4, B15C5 and B18C6 systems

In the aqueous-organic biphasic electromigration system, the larger cavity size of crown ethers, the weaker binding between crown ethers and Li+, and the lower dissociating voltage of complexes and initial voltage enriching 6Li in the catholyte.

Electromigration separation of lithium isotopes: The effect of ionic liquid ratios

This study is based on the system of “anodic aqueous solution | crown ether-ionic liquid organic solution | cathodic aqueous solution”, the influence of ionic liquid ratio in organic solution under different voltages on Li+ transport and lithium isotope separation was investigated. It is found that ionic liquids have multiple roles. In addition to improving the conductivity of organic solutions and enhancing Li+ transport capacity between aqueous solution and organic solution through ion exchange. Ionic liquids are even to realize the migration of lithium ions from aqueous solution to organic solution through solvation. There is an obvious synergistic enhancement between ionic liquid solvation and electric field. Based on this, three types of Li+ transport across the aqueous-organic interface are proposed. The influencing mechanism of ionic liquid ratio, voltage on Li+ migration ratio and lithium isotope separation is discussed in detail.

Effect of the Substrate and the Morphology on Electrochemical Separation of Lithium Isotopes: Insights from DFT

Effect of the Substrate and the Morphology on Electrochemical Separation of Lithium Isotopes: Insights from DFT

Lithium isotope separation by precipitation method coupled with solvent extraction with 1-Hydroxy-4-(p-toluidino) anthraquinone

This paper reported a novel chelating agent and a green precipitation-extraction separation strategy for lithium isotope enrichment. 1-Hydroxy-4-(p-toluidino) anthraquinone and anisole were used as chelating agent and diluent, respectively. Three phases including organic phase, aqueous phase and precipitation could be preparated. The experiment indicated that excess sodium hydroxide was helpful to promote the single-stage precipitation rate and equilibrium time. The isotope result indicated that 6Li was concentrated in the aqueous phase and 7Li was concentrated in precipitation phase. The maximum single-stage lithium isotope speration factor reached to 1.013 ± 0.001. By doing thermodynamic analysis of the reaction, the free energy change (ΔG), enthalpy change (ΔH) and entropy change(ΔS) of the separation process were −8.97 J mol−1, −21.37 J mol−1 and −0.0438 J mol−1 K−1 at 283 K. The results of DFT simulation and wave function analysis indicated that a lithium ion combined with a chelating agent anion formed a stable six-member ring between two oxygen, which was more stable than sodium ions combined with chelating agent anions (the Gibbs free energy of the lithium ions reaction was more negative). As interaction analysis result showed, the Li-O bond in complex interaction was significantly stronger than the Li-O bond interaction in aqueous phase, which was the theroy that led to the enrichment of 7Li in organic phase. In the activated carbon treatment experiment, it was found that part of lithium chelator solved in aqueous phase, which resulted in that the lithium abundance of aqueous phase hardly changed. In order to increase the abundance of 6Li in aqueous phase, it is necessary to add adjuvant to reduce the water solubility of lithium chelate. Overall, an economical and environmental-friendly precipitation method with a certain application prospect for lithium isotope separation was proposed, and the direction of improving the separation performance was pointed out in this paper.

New Trends in Separation Techniques of Lithium Isotopes: A Review of Chemical Separation Methods.

In terms of isotopic technologies, it is essential to be able to produce materials with an enriched isotopic abundance (i.e., a compound isotopic labelled with 2H, 13C, 6Li, 18O or 37Cl), which is one that differs from natural abundance. The isotopic-labelled compounds can be used to study different natural processes (like compounds labelled with 2H, 13C, or 18O), or they can be used to produce other isotopes as in the case of 6Li, which can be used to produce 3H, or to produce LiH that acts like a protection shield against fast neutrons. At the same time, 7Li isotope can be used as a pH controller in nuclear reactors. The COLEX process, which is currently the only technology available to produce 6Li at industrial scale, has environmental drawbacks due to generation of Hg waste and vapours. Therefore, there is a need for new eco-friendly technologies for separation of 6Li. The separation factor of 6Li/7Li with chemical extraction methods in two liquid phases using crown ethers is comparable to that of COLEX method, but has the disadvantages of low distribution coefficient of Li and the loss of crown ethers during the extraction. Electrochemical separation of lithium isotopes through the difference in migration rates between 6Li and 7Li is one of the green and promising alternatives for the separation of lithium isotopes, but this methodology requires complicated experimental setup and optimisation. Displacement chromatography methods like ion exchange in different experimental configurations have been also applied to enrich 6Li with promising results. Besides separation methods, there is also a need for development of new analysis methods (ICP-MS, MC-ICP-MS, TIMS) for reliable determination of Li isotope ratios upon enrichment. Considering all the above-mentioned facts, this paper will try to emphasize the current trends in separation techniques of lithium isotopes by exposing all the chemical separation and spectrometric analysis methods, and highlighting their advantages and disadvantages.

Electromigration separation of lithium isotopes: The effect of electrolytes

The high-abundance lithium isotopes are key materials for the development of the nuclear industry. Lithium amalgamation is currently the only industrial method used to produce lithium isotopes, but it involves serious environmental pollution. Electromigration separation is one of the green and promising alternatives. Here, a “lithium salt aqueous solution │ organic solution │ aqueous solution” electromigration system was fabricated for lithium isotope separation. At a higher or lower voltage, the effects of species and initial pH of catholyte on the separation effects of lithium isotopes during electromigration were studied with different migrate time, and the origin of isotope separation was discussed. It was found that the initial pH values of the catholyte had an effect on the pH values of the anolyte. While the dramatic variation of pH in the electrolyte during electromigration was averse to the migration of Li+ and isotope separation. Furthermore, an extremely high isotope separation coefficient (1.6) was obtained at a very low Li+ migration ratio that is based on the dynamic separation. While the separation coefficient decreases with the increase of Li+ migration ratio rapidly and finally levels off, that is based on the equilibrium separation. This work provides important guidance for understanding the electromigration process and the origin of isotope separation in this system.

Novel class of crown ether functionalized ionic liquids with multiple binding sites for efficient separation of lithium isotopes

Lithium isotopes (6Li, 7Li) separation is an industrially important but challenging process due to their very similar chemical and physical properties. Crown ethers (CEs) have great potential in the isotopes separation for their typical cavity structures. However, the low distribution of Li+ has restricted their industrialuse. In this work, a novel class of functionalized ionic liquids with grafted crown ether-moieties (CE-FILs) for efficient separation of 6Li and 7Li are first reported. The enhanced distribution of Li+ could be achieved by the synergistic effect of ion–dipole interaction, hydrogen bonding and coordination interaction. As a result, an exceptionally high distribution coefficient for Li+ (DLi, up to 136) is obtained using 0.3 M [C6(B15C5)mim][NTf2] with a satisfied separation factor of 1.034 (at 273 K) for 6Li/7Li selectivity from an extremely hydrophilic chloride solutions, which strikes an excellent balance between Li distribution and 6Li/7Li separation. Theoretical calculations and spectroscopic characterization confirm that [C6(B15C5)mim][NTf2] supplies as an ion pair receptor to bind Li+, forming a 1:1 ion-pair complex [C6(B15C5)mim][NTf2]…Li+FeCl4- with double cations and anions. The separation performance of 6Li/7Li mainly depends on the weak interactions associated with Li+. The CE-FILs pave a new way for Li isotopes separation.

Calix[4]arene-Decorated Covalent Organic Framework Conjugates for Lithium Isotope Separation.

Lithium isotope separation has attracted extensive interest due to its important role in fusion and fission reactions. Up to now, it is still a great challenge to separate lithium isotopes (6Li and 7Li) in an efficient manner due to the low capture ability for lithium ions of related materials and highly similar physicochemical properties between lithium isotopes. In this work, three calix[4]arene-decorated crystalline covalent organic frameworks (COFs) with wave-like extension and AA-stacking configuration were designed and utilized for lithium adsorption and its isotope separation. Experimental studies show that these COFs exhibit an outstanding lithium adsorption capacity up to 94.66 mg·g-1, which is about 2 times beyond that of adsorbents reported in the literature. The high adsorption capacity of COFs could be attributed to the abundant adsorption sites from calix[4]arene unit. More importantly, this study demonstrates for the first time that calixarene groups can separate lithium isotopes with an excellent separation factor up to 1.053 ± 0.002, comparable to the most successful solid-phase lithium separation adsorbent. The calculation based on density functional theory showed that calixarene played an important role in the lithium adsorption. Interestingly, the lithium isotope separation performance is mainly affected by the amine bridging units. This work demonstrated that calixarene COFs are promising adsorbents for lithium isotope separation.

The extraction method for the separation of lithium isotopes using B12C4/B15C5/B18C6-ionic liquid systems

B12C4 systems achieve better 6Li enrichment in the organic phase and B15C5 systems achieve better 7Li enrichment in the aqueous phase.

Dibenzo-15-crown-5-based Tröger's Base membrane for 6Li+/7Li+ separation

The separation of lithium isotopes through membrane-based technologies has become an increasingly attractive research direction, considering the application of lithium isotopes as potential energy sources. However, the very similar physicochemical properties of 6Li+ and 7Li+ pose a significant challenge in developing capable membranes and the separation performance is currently not satisfactory. Here we report a dibenzo-15-crown-5-based polymeric membrane synthesized from Tröger's Base (TB) polymerization, namely PIM-DB15C5-TB, for lithium isotope separations. The introduction of dibenzo-15-crown-5 enables PIM-DB15C5-TB to manifest good 6Li+/7Li+ selectivity, and the TB units having rigid and contorted structure conformation provide PIM-DB15C5-TB with abundant free volumes for 6Li+/7Li+ transport. When applied in electrodialysis for the separation of 6Li+/7Li+, PIM-DB15C5-TB demonstrates a 6Li+/7Li+ selectivity of 1.16. The current work proposes a strategy for developing polymeric membranes for the selective separation of lithium isotopes.

Solvent extraction for lithium isotope separation by 4-NO2-B15C5/[BMIm][NTf2] system

The evolution of the nuclear industry is inextricably linked to lithium isotopes. With its distinct benefits, the solvent extraction approach is projected to achieve industrial separation of lithium isotopes. However, the lack of studies on the extraction process conditions and mechanisms has limited the development of multi-stage processes. In this paper, based on the 4-NO2-B15C5/[BMIm][NTf2] system, the process conditions and extraction mechanism of the system were investigated by thermodynamic and kinetic studies. The results indicate that lithium isotope separation is a spontaneous exothermic process controlled by diffusion. In addition, DFT calculations show that the binding sites of crown ether and Li+ are located in the coronary heart of crown ether, and electrostatic and van der Waals forces mainly exist between them. On this basis, a 10-stage cross-flow extraction experiment was carried out using crown ether as the extractant. The aqueous phase feed solution is fully utilized, and the 7Li abundance is increased to 93.29 %. In summary, this research provides a foundation for the development of synergistic multi-stage extraction techniques in the future.

A new technique of lithium isotope extraction and separation: Flotation complexation extraction

Flotation complexation extraction can effectively extract and separate lithium isotopes. The effects of nitrogen flow rate, bubble size, gas holdup, reaction flow pattern, aeration time, and temperature on the separation process were studied. In addition, the complex relationship and separation mechanism of lithium with 10-hydroxybenzoquinoline were discussed. Results show that nitrogen flow rate and bubble size significantly affected the flotation complexation extraction process. With an appropriate flow rate, we obtained a homogeneous regime pattern containing small and evenly distributed bubbles to achieve better separation efficiency and ensure a smooth extraction process. According to the slope method, lithium and 10-hydroxybenzoquinoline were complexed and extracted at a ratio of 1: 2. Compared with the traditional oscillating extraction, the bubble mass transfer mode in the flotation complexation extraction strengthened the complex extraction process and achieved higher extraction rate and separation efficiency.

Extraction separation of lithium isotopes with Bromobenzene-15-crown-5/ionic liquids system: Experimental and theoretical study

Controlled fusion energy is considered to be one kind of sustainable energy source with clean and green properties. The fusion process requires a large number of lithium isotopes, but the naturally stable lithium isotopes 6Li and 7Li cannot be directly applied to the fusion process and must be further enriched. In this paper, a system for the separation of lithium isotopes by extraction was investigated, which mainly consists of bromobenzene-15-crown-5 and ionic liquids. The effects of ionic liquids, lithium salts, crown ether concentration, and temperature on the separation performance of lithium isotopes were explored. It was found that 6Li was enriched in the organic phase and the single-stage separation factor reached 1.032. It was proved by the temperature experiment that the exchange of lithium isotopes was a spontaneous and exothermic process. The complexation ratio of crown ether and lithium ions was 1:1. The optimized complexation model and the interaction of crown ether and lithium ions were calculated by DFT and Multiwfn. Lithium ions were weakly bonded to the crown ether and strongly bonded to the water molecule as demonstrated by the non-bonded interactions and Mayer bond order of Li-O. Meanwhile, the mechanism of lithium isotope separation with crown ether was clarified by mutual verification of experiment and theoretical calculations.

Experimental and theoretical investigations of lithium isotopes separation using 10-hydroxybenzoquinoline

Experimental and theoretical investigations of lithium isotopes separation using 10-hydroxybenzoquinoline

Separation of lithium isotopes: Electromigration coupling with crystallization

6Li and 7Li, two natural isotopes of lithium, play an important role in the nuclear industry. Here, a system of ionic liquid-crown ether was fabricated for lithium isotope separation and the 6Li isotope separation coefficient can reach 1.406 that showing a good prospect for lithium isotope separation by this method of electromigration. Interestingly, the single crystal containing crown ether and lithium, in which 7Li was enriched, was obtained from the experiments. It is contrary to popular wisdom and can be attributed to the steric hindrance effect. This provides a new route to separate lithium isotopes, that is electromigration coupling with crystallization.

Highly efficient lithium adsorption and stable isotope separation by metal-organic frameworks.

The effects of a series of MOFs on the adsorption and separation of lithium isotopes were investigated in this paper. Seven kinds of MOF were prepared, and the characterization studies of MIL-100(Fe) before and after adsorption by X-ray photoelectron spectroscopy (XPS) demonstrated the potential chemical interaction between Fe and Li. The influence of metal ions, counter-ions and solvents on the adsorption capacity and separation factor was investigated. The maximum separation factor can reach 1.048 ± 0.001. MIL-100(Fe) also has good regeneration performance.